U.S. patent number 4,377,748 [Application Number 06/142,703] was granted by the patent office on 1983-03-22 for x-ray diagnostic system comprising means for the fixed specification of exposure time, x-ray tube voltage, and mas-product.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Horst Aichinger, Gerd Seifert.
United States Patent |
4,377,748 |
Aichinger , et al. |
March 22, 1983 |
X-Ray diagnostic system comprising means for the fixed
specification of exposure time, x-ray tube voltage, and
mAs-product
Abstract
In an exemplary embodiment, a control loop for the x-ray tube
current is present which adjusts the x-ray tube current to a value
which is a function of the exposure time and the selected
mAs-product. In order that deviations of the x-ray tube voltage
from a desired value can be controlled via the x-ray tube current,
but that the mean value of the x-ray tube current can nevertheless
be kept constant, a phase angle control device, arranged in the
primary circuit of the high voltage transformer, can be present as
the regulating unit for the mean value of the x-ray tube current.
As controller for the x-ray tube voltage, a circuit for the
adjustment of the filament current of the x-ray tube can be
provided.
Inventors: |
Aichinger; Horst (Fuerth,
DE), Seifert; Gerd (Spardorf, DE) |
Assignee: |
Siemens Aktiengesellschaft
(Berlin & Munich, DE)
|
Family
ID: |
6070124 |
Appl.
No.: |
06/142,703 |
Filed: |
April 22, 1980 |
Foreign Application Priority Data
Current U.S.
Class: |
378/110 |
Current CPC
Class: |
H05G
1/46 (20130101); H05G 1/34 (20130101) |
Current International
Class: |
H05G
1/00 (20060101); H05G 1/34 (20060101); H05G
1/46 (20060101); H05G 001/34 () |
Field of
Search: |
;250/415,409,413,421 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Smith; Alfred E.
Assistant Examiner: Grigsby; T. N.
Attorney, Agent or Firm: Hill, Van Santen, Steadman, Chiara
& Simpson
Claims
We claim as our invention:
1. An x-ray diagnostic system comprising an x-ray tube for
supplying x-ray energy at a film plane, supply means for supplying
x-ray tube voltage to said x-ray tube, means for the fixed
specification of the exposure time of an x-ray photograph, and
adjustment means for selecting the x-ray tube voltage and the
mAs-product, characterized in that an x-ray tube current control
loop for controlling the x-ray tube current is present which
controls the x-ray tube current on the basis of the fixed exposure
time and the selected mAs-product, said x-ray tube current control
loop comprising actual x-ray tube current sensing means for sensing
the actual value of x-ray tube current, x-ray tube current setpoint
means controlled in accordance with the fixed specification of the
exposure time, and being operable in conjunction with the
adjustment means for selecting mAs-product, to provide a
corresponding setpoint value of x-ray tube current, and x-ray tube
current control means for controlling the x-ray tube current and
responsive to deviations of the actual x-ray tube current as sensed
by said actual x-ray tube current sensing means, from the setpoint
value of x-ray tube current as provided by said x-ray tube current
setpoint means, to tend to maintain the actual value of x-ray tube
current at said setpoint value, said supply means comprising a high
voltage transformer (6) having a primary circuit, and said x-ray
tube current control loop comprising a keying circuit (23) for
controlling the x-ray tube current, arranged in the primary circuit
of the high voltage transformer (7).
2. An x-ray diagnostic system according to claim 1, characterized
in that the keying circuit is formed by a phase angle controller
(23).
3. An x-ray diagnostic system according to claim 1, characterized
in that the keying circuit exhibits an electronic switch which is
actuated with a pulse duty factor which corresponds to the desired
x-ray tube current and which is operated synchronized by the power
supply (or mains) such that the peak value of the x-ray tube
voltage remains constant in the case of change of the pulse duty
factor and which electronic switch is disposed in the d.c. current
branch of a rectifier bridge in the primary circuit.
4. An x-ray diagnostic system according to claim 1, characterized
in that control loop means (10 through 14) for controlling the
x-ray tube voltage is present.
5. An x-ray diagnostic system according to claim 4 characterized in
that, the control loop means (10 through 14) for the x-ray tube
voltage comprises a setpoint value transmitter circuit (11)
connected with said x-ray tube current control loop (17-23) for
receiving a phase angle control signal (.alpha.) therefrom, and
being responsive to said phase angle signal (.alpha.) to correct
the setpoint value for x-ray tube voltage for obtaining a fixed
dose in the film plane.
6. An x-ray diagnostic system according to claim 4, characterized
in that said control loop means is operative for adjustment of the
filament current of the x-ray tube (1), so that the voltage drop in
the supply means (2-7) brought about by the x-ray tube current,
becomes so adjusted that the desired x-ray tube voltage is
present.
7. An x-ray diagnostic system according to claim 6, characterized
in that, the control loop means (10 through 14) for the x-ray tube
voltage comprises a setpoint value transmitter circuit (11)
connected with said x-ray tube current control loop (17-23) for
receiving a phase angle control signal (.alpha.) therefrom, and
being responsive to said phase angle signal (.alpha.) to correct
the setpoint value for x-ray tube voltage for obtaining a fixed
dose in the film plane.
Description
BACKGROUND OF THE INVENTION
The invention relates to an x-ray diagnostic system comprising
means for the fixed specification of the exposure time of an x-ray
photograph, as well as comprising adjustment means for selecting
the setting of the x-ray tube voltage and the mAs-product.
An x-ray diagnostic system of this type is described in the German
AS No. 2,116,705. The exposure time is here specified by a
planigraphic apparatus for preparation of x-ray laminograms and is
determined by the selected movement path of the x-ray tube and of
the image layer carrier. In the case of the known x-ray diagnostic
system, the computer determines, from the specified exposure time
and the adjusted mAs-product, the necessary x-ray tube current and
effects its adjustment in the x-ray diagnostic generator. In the
case of an x-ray generator wherein the adjustment of the x-ray tube
voltage proceeds via the filament current of the x-ray tube and the
voltage drop at the generator internal resistance, brought about
thereby, one is however, not free, with fixedly specified values
for x-ray tube voltage, mAs-product, and exposure time, with regard
to selection of the x-ray tube current; on the contrary, one is
restricted to the operating points specified by the voltage drop
curves. In addition, an exact observance of the adjusted
mAs-product is not guaranteed in the case of a generator which
determines the x-ray tube current via a computer circuit from
mAs-product and exposure time and fixedly adjusts said x-ray tube
current prior to the photographic exposure, since fluctuations of
the x-ray tube current arising during a photographic exposure
cannot be taken into account.
SUMMARY OF THE INVENTION
The object underlying the invention resides in designing an x-ray
diagnostic system of the type initially cited such that the
selected mAs-product is also exactly observed within the specified
time.
This object is achieved in accordance with the invention by virtue
of the fact that a control loop for controlling the x-ray tube
current is present which controls the x-ray tube current on the
basis of the fixed exposure time and the selected mAs-product. In
the inventive x-ray diagnostic system the control loop for the
x-ray tube current acts, in conjunction with the selection means
for the mAs-product, as an mAs-control unit. The adjusted
mAs-product is precisely observed during a photographic exposure
due to deviation (error responsive) control.
A particularly expedient embodiment of the invention consists in
that, for controlling the x-ray tube current, a keying circuit,
arranged in the primary circuit of the high voltage transformer, is
provided. Via this keying circuit the mean value of the x-ray tube
current can be altered e.g. through influencing of the phase angle.
It is thus possible to provide a control loop for the x-ray tube
voltage which exhibits, as the control element, means for the
adjustment of the filament current of the x-ray tube, so that the
voltage drop in the x-ray diagnostic generator brought about by the
x-ray tube current becomes so adjusted that the desired x-ray tube
voltage is present. In this further development, deviations of the
x-ray tube voltage from its desired (setpoint) value are controlled
via the x-ray tube current and the voltage drop brought about
thereby in the alternating current supply circuit (before the
direct current x-ray tube circuit). The mean value of the x-ray
tube current can be kept constant, independently of the control of
x-ray tube voltage fluctuations, via the phase-angle control
device, since, in the case of a change of the phase-angle, the mean
value of the x-ray tube current and the peak value of the x-ray
tube voltage do not run proportionally to one another. In case also
the peak value of the x-ray tube voltage drops via the phase-angle
and the altered waveform of the x-ray tube voltage connected
therewith, the control element for the filament current intervenes
and again returns the peak value of the x-ray tube voltage to the
initial value.
The dose in the film plane is dependent not only upon the x-ray
tube peak voltage and the selected mAs-value, but also upon the
waveform of the x-ray tube voltage which likewise changes in case
of a change in the phase angle. This behavior can be taken into
account by a correction of the adjusted desired (setpoint) value
for the x-ray tube voltage, in dependence upon the phase-angle,
with the object of obtaining a fixed dose in the film plane which
dose is independent of the waveform of the x-ray tube voltage.
The invention is explained in greater detail below on the basis of
an exemplary embodiment illustrated on the accompanying drawing
sheet; and other objects, features and advantages will be apparent
from this detailed disclosure and from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the circuit diagram of an x-ray diagnostic system
according to the invention; and
FIG. 2 shows a graphic illustration useful in explaining the
operation of the embodiment of FIG. 1.
DETAILED DESCRIPTION
In FIG. 1 an x-ray tube 1 is shown which receives its high voltage
from two high voltage rectifiers 2 and 3, connected in series
relative to one another, which rectifiers are supplied by two
secondary winding groups 4 and 5 of a three-phase-high-voltage
transformer 6. The supply of the primary winding group 7 of the
high voltage transformer 6 proceeds via a switch cabinet 8 from the
three-phase mains. The filament current for the x-ray tube 1 is
supplied by a filament transformer 9 which is connected to a
control element 10 for controlling the filament current. The
filament current control circuit 10 is activated by the output
signal of a kV-control circuit 10a which possesses a desired (or
setpoint) value input 12 and an actual value input 13. The actual
value signal for the x-ray tube voltage is tapped at a voltage
divider 14 in the high voltage circuit. The desired or setpoint
value signal for the KV-control unit 10a is supplied by a setpoint
value transmitter 11 which receives the KV-desired value from the
switch cabinet 8 via the input 12a.
In the example the exposure time is specified by the selected
movement path of an x-ray planigraphic apparatus 15. A signal
corresponding to the fixed exposure time is supplied to one input
15' of the switch cabinet 8. On the switch cabinet 8, adjustment
means for the mAs-product and the x-ray tube voltage are present.
The adjustment means for the x-ray tube voltage produces the signal
for the input 12a. The exposure time is controlled by a time switch
16 which is activated by the signal at input 15' of the switch
cabinet 8.
The illustrated x-ray diagnostic system possesses an x-ray tube
current control unit 17 to which a desired value signal is supplied
at the input 18 and an actual value signal for the x-ray tube
current is supplied at the input 19. The actual value signal is
tapped on a series resistance 20 in the high voltage circuit
between the two high voltage rectifiers 2 and 3. The desired value
signal at the input 18 can be generated by a setpoint value circuit
21 which determines the desired value signal from the adjusted
mAs-product and the specified exposure time. In the illustrated
example, however, only one mA-desired value is formed for every
time value. The mAs-gradation proceeds by means of a corresponding
amplification switch-over of the x-ray tube current control unit
17.
The output signal of the x-ray tube current control unit 17, which
corresponds to the difference between the actual- and desired-value
of the x-ray tube current, is supplied to a PI-control unit 17a
which, via a line 22, activates a phase angle control device 23 in
the primary circuit of the high voltage transformer and determines
the phase angle .alpha., at which the mains voltage is
through-connected to the high voltage transformer 6. The phase
angle controller 23 is switched on in the two phases R and S and is
synchronized by the phases R and T. A phase angle control device
which can be employed here is described in the German Pat. No.
2,401,774 and in the corresponding U.S. Pat. No. 3,978,339. The
phase angle .alpha. is altered upon occurrence of a difference
between the desired value and the actual value of the x-ray tube
current until this difference is zero.
Within a predetermined range up to a phase angle of 120.degree. the
mean value of the x-ray tube current can be altered via the
phase-angle without the peak value of the x-ray tube current being
changed. If this range is exceeded, then, in the case of a further
change of the phase-angle, in addition to the mean value of the
x-ray tube current changing, also the peak value of the x-ray tube
voltage changes. The kV-control unit device 10a becomes effective
and influences, via the control element 10, the filament current of
the x-ray tube 1 and hence additionally the x-ray tube current.
This additional x-ray tube current change must again be compensated
via an additional change in the phase-angle of the phase angle
control device 23. Thus, in the steady state of the control loop,
x-ray tube current and x-ray tube voltage always correspond to the
adjusted desired values.
In order to correct the dose change in the film plane in the case
of a change of the waveform of the x-ray tube voltage, the desired
value for the x-ray tube voltage, supplied by the switch cabinet 8,
is corrected via input 24 to kV setpoint value transmitter 11 in
dependence upon the phase-angle .alpha., with the object of a dose
correction in the setpoint value transmitter 11.
The basic adjustment of the x-ray tube current (operating point I,
FIG. 2) prior to an exposure can take place via the control element
10. The filament current of the x-ray tube 1 is here a function of
the selected load line, of the selected mAs-product, and the
selected x-ray tube voltage. The transition from operating point I
to the necessary operating point II proceeds via the phase angle
control device 23.
Instead of the phase angle control device 23, also an electronic
switch can be provided as a key switch which is operated with a
pulse-duty factor which corresponds to the mean value of the x-ray
tube current, necessary for the desired mAs-product, and which is
activated synchronized by the mains (or power supply) such that the
peak value of the x-ray tube voltage remains constant in the case
of change of the pulse duty factor and which switch is disposed in
the d.c. current branch of a rectifier bridge in the primary
circuit.
For the keying of the x-ray tube current, means can also be
provided for controlling the grid of a triode x-ray tube with a
suitable voltage; for example, voltage pulses.
The control of the x-ray tube voltage can also proceed via a triode
in the high voltage circuit of the x-ray diagnostic generator at
which the voltage drop is adjusted via a control voltage such that
the desired x-ray tube voltage is present. In this case, the
control of the x-ray tube current can take place via the filament
current by means of continuous alteration of the x-ray tube
current. However, instead of control of the x-ray tube voltage via
a triode in the high voltage circuit, it is also possible to
control the x-ray tube voltage via a continuously variable grid
bias voltage of a grid-controlled x-ray tube.
It will be apparent that many modifications and variations may be
effected without departing from the scope of the novel concepts and
teachings of the present invention.
* * * * *